HoFo user awwong just dropped me a note that the OTA Jellybean update for the Nexus S was just pushed out.
Did you get yours yet?
I've updated my Nexus S (T-Mobile, Wind AWS variant) to Android 4.1.1 Jelly Bean a few hours ago and have been testing it. So far I like the taste of it! I connected to wifi to make the download faster.